The Tire Pressure Monitoring System (TPMS) was created to warn you that one or more of your tires is under-inflated, which presents a possibly unsafe driving condition. The indicator light is a yellow cross-section of a tire with an exclamation mark in the middle. When this symbol lights up on your dashboard, it is reminding you that you have low pressure, which will hopefully instill in your mind the importance of keeping your tire pressure at a safe level.
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The need for the TPMS came from a rise in serious (and avoidable) accidents that occurred because drivers did not know that their tires were under-inflated. Before the introduction of the TPMS, drivers had to get out of their vehicles and check each tire using the only tool at their disposal: a tire gauge.
In 2007, the U.S. government passed the Transportation Recall Enhancement, Accountability, and Documentation Act (TREAD) that required vehicle manufacturers to fit vehicles with a tire pressure monitoring system. They argued that if drivers had an easier way of knowing the pressure of their tires, accidents could be avoided. The introduction of the TPMS has significantly reduced the number of vehicular accidents caused by under-inflated tires.
Two different types of TPMS are in use today: Direct TPMS and Indirect TPMS. Direct TPMS utilizes a wheel-mounted sensor to monitor air pressure in each of the tires. The sensor transmits the information to the car’s computer system if the air pressure drops 25% below the recommended level. The computer system will then trigger the dashboard indicator light, which will serve as a warning to the driver that one or more of his tires are under-inflated.
The indirect TPMS works with the wheel speed sensors mounted to the anti-lock braking system. Tires with low pressure make a full revolution at a different rate than properly inflated tires. When your system notes that there is a discrepancy between the tire rotation speeds, it will turn on the dashboard’s indicator light.
The direct TPMS and the indirect TPMS have advantages and disadvantages, but they both work for the safety of the driver. The car manufacturers decide on which system to include in the vehicles they produce based on their assessment of what will be best for the safety of the driver and the passengers.
If you notice that the TPMS indicator light is illuminated on your dashboard, you should check the pressure on each of your tires. Make sure to check them first thing in the morning when the tires are cool or after the car has been at rest for at least an hour. Only fill tires to the recommended psi that is found on the inside driver’s door because overinflating can cause other problems.
Although the methods of monitoring tire pressure are different, both the Direct TPMS and Indirect TPMS serve the same purpose of monitoring tire pressure and activating the indicator light located on the dashboard. However, drivers should not get complacent and rely solely on the TPMS. It is still important for drivers to periodically get their hands dirty and manually check the pressure of their tires using a tire gauge. Drivers should make it a habit to regularly check the vehicle’s tire pressure, especially before embarking on a long trip.